| 1 | =head1 NAME |
| 2 | |
| 3 | perlembed - how to embed perl in your C program |
| 4 | |
| 5 | =head1 DESCRIPTION |
| 6 | |
| 7 | =head2 PREAMBLE |
| 8 | |
| 9 | Do you want to: |
| 10 | |
| 11 | =over 5 |
| 12 | |
| 13 | =item B<Use C from Perl?> |
| 14 | |
| 15 | Read L<perlxstut>, L<perlxs>, L<h2xs>, L<perlguts>, and L<perlapi>. |
| 16 | |
| 17 | =item B<Use a Unix program from Perl?> |
| 18 | |
| 19 | Read about back-quotes and about C<system> and C<exec> in L<perlfunc>. |
| 20 | |
| 21 | =item B<Use Perl from Perl?> |
| 22 | |
| 23 | Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlfunc/require> |
| 24 | and L<perlfunc/use>. |
| 25 | |
| 26 | =item B<Use C from C?> |
| 27 | |
| 28 | Rethink your design. |
| 29 | |
| 30 | =item B<Use Perl from C?> |
| 31 | |
| 32 | Read on... |
| 33 | |
| 34 | =back |
| 35 | |
| 36 | =head2 ROADMAP |
| 37 | |
| 38 | =over 5 |
| 39 | |
| 40 | =item * |
| 41 | |
| 42 | Compiling your C program |
| 43 | |
| 44 | =item * |
| 45 | |
| 46 | Adding a Perl interpreter to your C program |
| 47 | |
| 48 | =item * |
| 49 | |
| 50 | Calling a Perl subroutine from your C program |
| 51 | |
| 52 | =item * |
| 53 | |
| 54 | Evaluating a Perl statement from your C program |
| 55 | |
| 56 | =item * |
| 57 | |
| 58 | Performing Perl pattern matches and substitutions from your C program |
| 59 | |
| 60 | =item * |
| 61 | |
| 62 | Fiddling with the Perl stack from your C program |
| 63 | |
| 64 | =item * |
| 65 | |
| 66 | Maintaining a persistent interpreter |
| 67 | |
| 68 | =item * |
| 69 | |
| 70 | Maintaining multiple interpreter instances |
| 71 | |
| 72 | =item * |
| 73 | |
| 74 | Using Perl modules, which themselves use C libraries, from your C program |
| 75 | |
| 76 | =item * |
| 77 | |
| 78 | Embedding Perl under Win32 |
| 79 | |
| 80 | =back |
| 81 | |
| 82 | =head2 Compiling your C program |
| 83 | |
| 84 | If you have trouble compiling the scripts in this documentation, |
| 85 | you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY |
| 86 | THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.) |
| 87 | |
| 88 | Also, every C program that uses Perl must link in the I<perl library>. |
| 89 | What's that, you ask? Perl is itself written in C; the perl library |
| 90 | is the collection of compiled C programs that were used to create your |
| 91 | perl executable (I</usr/bin/perl> or equivalent). (Corollary: you |
| 92 | can't use Perl from your C program unless Perl has been compiled on |
| 93 | your machine, or installed properly--that's why you shouldn't blithely |
| 94 | copy Perl executables from machine to machine without also copying the |
| 95 | I<lib> directory.) |
| 96 | |
| 97 | When you use Perl from C, your C program will--usually--allocate, |
| 98 | "run", and deallocate a I<PerlInterpreter> object, which is defined by |
| 99 | the perl library. |
| 100 | |
| 101 | If your copy of Perl is recent enough to contain this documentation |
| 102 | (version 5.002 or later), then the perl library (and I<EXTERN.h> and |
| 103 | I<perl.h>, which you'll also need) will reside in a directory |
| 104 | that looks like this: |
| 105 | |
| 106 | /usr/local/lib/perl5/your_architecture_here/CORE |
| 107 | |
| 108 | or perhaps just |
| 109 | |
| 110 | /usr/local/lib/perl5/CORE |
| 111 | |
| 112 | or maybe something like |
| 113 | |
| 114 | /usr/opt/perl5/CORE |
| 115 | |
| 116 | Execute this statement for a hint about where to find CORE: |
| 117 | |
| 118 | perl -MConfig -e 'print $Config{archlib}' |
| 119 | |
| 120 | Here's how you'd compile the example in the next section, |
| 121 | L<Adding a Perl interpreter to your C program>, on my Linux box: |
| 122 | |
| 123 | % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include |
| 124 | -I/usr/local/lib/perl5/i586-linux/5.003/CORE |
| 125 | -L/usr/local/lib/perl5/i586-linux/5.003/CORE |
| 126 | -o interp interp.c -lperl -lm |
| 127 | |
| 128 | (That's all one line.) On my DEC Alpha running old 5.003_05, the |
| 129 | incantation is a bit different: |
| 130 | |
| 131 | % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include |
| 132 | -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE |
| 133 | -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib |
| 134 | -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm |
| 135 | |
| 136 | How can you figure out what to add? Assuming your Perl is post-5.001, |
| 137 | execute a C<perl -V> command and pay special attention to the "cc" and |
| 138 | "ccflags" information. |
| 139 | |
| 140 | You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for |
| 141 | your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what |
| 142 | to use. |
| 143 | |
| 144 | You'll also have to choose the appropriate library directory |
| 145 | (I</usr/local/lib/...>) for your machine. If your compiler complains |
| 146 | that certain functions are undefined, or that it can't locate |
| 147 | I<-lperl>, then you need to change the path following the C<-L>. If it |
| 148 | complains that it can't find I<EXTERN.h> and I<perl.h>, you need to |
| 149 | change the path following the C<-I>. |
| 150 | |
| 151 | You may have to add extra libraries as well. Which ones? |
| 152 | Perhaps those printed by |
| 153 | |
| 154 | perl -MConfig -e 'print $Config{libs}' |
| 155 | |
| 156 | Provided your perl binary was properly configured and installed the |
| 157 | B<ExtUtils::Embed> module will determine all of this information for |
| 158 | you: |
| 159 | |
| 160 | % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
| 161 | |
| 162 | If the B<ExtUtils::Embed> module isn't part of your Perl distribution, |
| 163 | you can retrieve it from |
| 164 | http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils/ |
| 165 | (If this documentation came from your Perl distribution, then you're |
| 166 | running 5.004 or better and you already have it.) |
| 167 | |
| 168 | The B<ExtUtils::Embed> kit on CPAN also contains all source code for |
| 169 | the examples in this document, tests, additional examples and other |
| 170 | information you may find useful. |
| 171 | |
| 172 | =head2 Adding a Perl interpreter to your C program |
| 173 | |
| 174 | In a sense, perl (the C program) is a good example of embedding Perl |
| 175 | (the language), so I'll demonstrate embedding with I<miniperlmain.c>, |
| 176 | included in the source distribution. Here's a bastardized, non-portable |
| 177 | version of I<miniperlmain.c> containing the essentials of embedding: |
| 178 | |
| 179 | #include <EXTERN.h> /* from the Perl distribution */ |
| 180 | #include <perl.h> /* from the Perl distribution */ |
| 181 | |
| 182 | static PerlInterpreter *my_perl; /*** The Perl interpreter ***/ |
| 183 | |
| 184 | int main(int argc, char **argv, char **env) |
| 185 | { |
| 186 | PERL_SYS_INIT3(&argc,&argv,&env); |
| 187 | my_perl = perl_alloc(); |
| 188 | perl_construct(my_perl); |
| 189 | PL_exit_flags |= PERL_EXIT_DESTRUCT_END; |
| 190 | perl_parse(my_perl, NULL, argc, argv, (char **)NULL); |
| 191 | perl_run(my_perl); |
| 192 | perl_destruct(my_perl); |
| 193 | perl_free(my_perl); |
| 194 | PERL_SYS_TERM(); |
| 195 | } |
| 196 | |
| 197 | Notice that we don't use the C<env> pointer. Normally handed to |
| 198 | C<perl_parse> as its final argument, C<env> here is replaced by |
| 199 | C<NULL>, which means that the current environment will be used. |
| 200 | |
| 201 | The macros PERL_SYS_INIT3() and PERL_SYS_TERM() provide system-specific |
| 202 | tune up of the C runtime environment necessary to run Perl interpreters; |
| 203 | they should only be called once regardless of how many interpreters you |
| 204 | create or destroy. Call PERL_SYS_INIT3() before you create your first |
| 205 | interpreter, and PERL_SYS_TERM() after you free your last interpreter. |
| 206 | |
| 207 | Since PERL_SYS_INIT3() may change C<env>, it may be more appropriate to |
| 208 | provide C<env> as an argument to perl_parse(). |
| 209 | |
| 210 | Also notice that no matter what arguments you pass to perl_parse(), |
| 211 | PERL_SYS_INIT3() must be invoked on the C main() argc, argv and env and |
| 212 | only once. |
| 213 | |
| 214 | Now compile this program (I'll call it I<interp.c>) into an executable: |
| 215 | |
| 216 | % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
| 217 | |
| 218 | After a successful compilation, you'll be able to use I<interp> just |
| 219 | like perl itself: |
| 220 | |
| 221 | % interp |
| 222 | print "Pretty Good Perl \n"; |
| 223 | print "10890 - 9801 is ", 10890 - 9801; |
| 224 | <CTRL-D> |
| 225 | Pretty Good Perl |
| 226 | 10890 - 9801 is 1089 |
| 227 | |
| 228 | or |
| 229 | |
| 230 | % interp -e 'printf("%x", 3735928559)' |
| 231 | deadbeef |
| 232 | |
| 233 | You can also read and execute Perl statements from a file while in the |
| 234 | midst of your C program, by placing the filename in I<argv[1]> before |
| 235 | calling I<perl_run>. |
| 236 | |
| 237 | =head2 Calling a Perl subroutine from your C program |
| 238 | |
| 239 | To call individual Perl subroutines, you can use any of the B<call_*> |
| 240 | functions documented in L<perlcall>. |
| 241 | In this example we'll use C<call_argv>. |
| 242 | |
| 243 | That's shown below, in a program I'll call I<showtime.c>. |
| 244 | |
| 245 | #include <EXTERN.h> |
| 246 | #include <perl.h> |
| 247 | |
| 248 | static PerlInterpreter *my_perl; |
| 249 | |
| 250 | int main(int argc, char **argv, char **env) |
| 251 | { |
| 252 | char *args[] = { NULL }; |
| 253 | PERL_SYS_INIT3(&argc,&argv,&env); |
| 254 | my_perl = perl_alloc(); |
| 255 | perl_construct(my_perl); |
| 256 | |
| 257 | perl_parse(my_perl, NULL, argc, argv, NULL); |
| 258 | PL_exit_flags |= PERL_EXIT_DESTRUCT_END; |
| 259 | |
| 260 | /*** skipping perl_run() ***/ |
| 261 | |
| 262 | call_argv("showtime", G_DISCARD | G_NOARGS, args); |
| 263 | |
| 264 | perl_destruct(my_perl); |
| 265 | perl_free(my_perl); |
| 266 | PERL_SYS_TERM(); |
| 267 | } |
| 268 | |
| 269 | where I<showtime> is a Perl subroutine that takes no arguments (that's the |
| 270 | I<G_NOARGS>) and for which I'll ignore the return value (that's the |
| 271 | I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>. |
| 272 | |
| 273 | I'll define the I<showtime> subroutine in a file called I<showtime.pl>: |
| 274 | |
| 275 | print "I shan't be printed."; |
| 276 | |
| 277 | sub showtime { |
| 278 | print time; |
| 279 | } |
| 280 | |
| 281 | Simple enough. Now compile and run: |
| 282 | |
| 283 | % cc -o showtime showtime.c \ |
| 284 | `perl -MExtUtils::Embed -e ccopts -e ldopts` |
| 285 | % showtime showtime.pl |
| 286 | 818284590 |
| 287 | |
| 288 | yielding the number of seconds that elapsed between January 1, 1970 |
| 289 | (the beginning of the Unix epoch), and the moment I began writing this |
| 290 | sentence. |
| 291 | |
| 292 | In this particular case we don't have to call I<perl_run>, as we set |
| 293 | the PL_exit_flag PERL_EXIT_DESTRUCT_END which executes END blocks in |
| 294 | perl_destruct. |
| 295 | |
| 296 | If you want to pass arguments to the Perl subroutine, you can add |
| 297 | strings to the C<NULL>-terminated C<args> list passed to |
| 298 | I<call_argv>. For other data types, or to examine return values, |
| 299 | you'll need to manipulate the Perl stack. That's demonstrated in |
| 300 | L<Fiddling with the Perl stack from your C program>. |
| 301 | |
| 302 | =head2 Evaluating a Perl statement from your C program |
| 303 | |
| 304 | Perl provides two API functions to evaluate pieces of Perl code. |
| 305 | These are L<perlapi/eval_sv> and L<perlapi/eval_pv>. |
| 306 | |
| 307 | Arguably, these are the only routines you'll ever need to execute |
| 308 | snippets of Perl code from within your C program. Your code can be as |
| 309 | long as you wish; it can contain multiple statements; it can employ |
| 310 | L<perlfunc/use>, L<perlfunc/require>, and L<perlfunc/do> to |
| 311 | include external Perl files. |
| 312 | |
| 313 | I<eval_pv> lets us evaluate individual Perl strings, and then |
| 314 | extract variables for coercion into C types. The following program, |
| 315 | I<string.c>, executes three Perl strings, extracting an C<int> from |
| 316 | the first, a C<float> from the second, and a C<char *> from the third. |
| 317 | |
| 318 | #include <EXTERN.h> |
| 319 | #include <perl.h> |
| 320 | |
| 321 | static PerlInterpreter *my_perl; |
| 322 | |
| 323 | main (int argc, char **argv, char **env) |
| 324 | { |
| 325 | char *embedding[] = { "", "-e", "0" }; |
| 326 | |
| 327 | PERL_SYS_INIT3(&argc,&argv,&env); |
| 328 | my_perl = perl_alloc(); |
| 329 | perl_construct( my_perl ); |
| 330 | |
| 331 | perl_parse(my_perl, NULL, 3, embedding, NULL); |
| 332 | PL_exit_flags |= PERL_EXIT_DESTRUCT_END; |
| 333 | perl_run(my_perl); |
| 334 | |
| 335 | /** Treat $a as an integer **/ |
| 336 | eval_pv("$a = 3; $a **= 2", TRUE); |
| 337 | printf("a = %d\n", SvIV(get_sv("a", 0))); |
| 338 | |
| 339 | /** Treat $a as a float **/ |
| 340 | eval_pv("$a = 3.14; $a **= 2", TRUE); |
| 341 | printf("a = %f\n", SvNV(get_sv("a", 0))); |
| 342 | |
| 343 | /** Treat $a as a string **/ |
| 344 | eval_pv( |
| 345 | "$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE); |
| 346 | printf("a = %s\n", SvPV_nolen(get_sv("a", 0))); |
| 347 | |
| 348 | perl_destruct(my_perl); |
| 349 | perl_free(my_perl); |
| 350 | PERL_SYS_TERM(); |
| 351 | } |
| 352 | |
| 353 | All of those strange functions with I<sv> in their names help convert Perl |
| 354 | scalars to C types. They're described in L<perlguts> and L<perlapi>. |
| 355 | |
| 356 | If you compile and run I<string.c>, you'll see the results of using |
| 357 | I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and |
| 358 | I<SvPV()> to create a string: |
| 359 | |
| 360 | a = 9 |
| 361 | a = 9.859600 |
| 362 | a = Just Another Perl Hacker |
| 363 | |
| 364 | In the example above, we've created a global variable to temporarily |
| 365 | store the computed value of our eval'ed expression. It is also |
| 366 | possible and in most cases a better strategy to fetch the return value |
| 367 | from I<eval_pv()> instead. Example: |
| 368 | |
| 369 | ... |
| 370 | SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE); |
| 371 | printf("%s\n", SvPV_nolen(val)); |
| 372 | ... |
| 373 | |
| 374 | This way, we avoid namespace pollution by not creating global |
| 375 | variables and we've simplified our code as well. |
| 376 | |
| 377 | =head2 Performing Perl pattern matches and substitutions from your C program |
| 378 | |
| 379 | The I<eval_sv()> function lets us evaluate strings of Perl code, so we can |
| 380 | define some functions that use it to "specialize" in matches and |
| 381 | substitutions: I<match()>, I<substitute()>, and I<matches()>. |
| 382 | |
| 383 | I32 match(SV *string, char *pattern); |
| 384 | |
| 385 | Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which |
| 386 | in your C program might appear as "/\\b\\w*\\b/"), match() |
| 387 | returns 1 if the string matches the pattern and 0 otherwise. |
| 388 | |
| 389 | int substitute(SV **string, char *pattern); |
| 390 | |
| 391 | Given a pointer to an C<SV> and an C<=~> operation (e.g., |
| 392 | C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string |
| 393 | within the C<SV> as according to the operation, returning the number of |
| 394 | substitutions made. |
| 395 | |
| 396 | SSize_t matches(SV *string, char *pattern, AV **matches); |
| 397 | |
| 398 | Given an C<SV>, a pattern, and a pointer to an empty C<AV>, |
| 399 | matches() evaluates C<$string =~ $pattern> in a list context, and |
| 400 | fills in I<matches> with the array elements, returning the number of matches |
| 401 | found. |
| 402 | |
| 403 | Here's a sample program, I<match.c>, that uses all three (long lines have |
| 404 | been wrapped here): |
| 405 | |
| 406 | #include <EXTERN.h> |
| 407 | #include <perl.h> |
| 408 | |
| 409 | static PerlInterpreter *my_perl; |
| 410 | |
| 411 | /** my_eval_sv(code, error_check) |
| 412 | ** kinda like eval_sv(), |
| 413 | ** but we pop the return value off the stack |
| 414 | **/ |
| 415 | SV* my_eval_sv(SV *sv, I32 croak_on_error) |
| 416 | { |
| 417 | dSP; |
| 418 | SV* retval; |
| 419 | |
| 420 | |
| 421 | PUSHMARK(SP); |
| 422 | eval_sv(sv, G_SCALAR); |
| 423 | |
| 424 | SPAGAIN; |
| 425 | retval = POPs; |
| 426 | PUTBACK; |
| 427 | |
| 428 | if (croak_on_error && SvTRUE(ERRSV)) |
| 429 | croak(SvPVx_nolen(ERRSV)); |
| 430 | |
| 431 | return retval; |
| 432 | } |
| 433 | |
| 434 | /** match(string, pattern) |
| 435 | ** |
| 436 | ** Used for matches in a scalar context. |
| 437 | ** |
| 438 | ** Returns 1 if the match was successful; 0 otherwise. |
| 439 | **/ |
| 440 | |
| 441 | I32 match(SV *string, char *pattern) |
| 442 | { |
| 443 | SV *command = newSV(0), *retval; |
| 444 | |
| 445 | sv_setpvf(command, "my $string = '%s'; $string =~ %s", |
| 446 | SvPV_nolen(string), pattern); |
| 447 | |
| 448 | retval = my_eval_sv(command, TRUE); |
| 449 | SvREFCNT_dec(command); |
| 450 | |
| 451 | return SvIV(retval); |
| 452 | } |
| 453 | |
| 454 | /** substitute(string, pattern) |
| 455 | ** |
| 456 | ** Used for =~ operations that |
| 457 | ** modify their left-hand side (s/// and tr///) |
| 458 | ** |
| 459 | ** Returns the number of successful matches, and |
| 460 | ** modifies the input string if there were any. |
| 461 | **/ |
| 462 | |
| 463 | I32 substitute(SV **string, char *pattern) |
| 464 | { |
| 465 | SV *command = newSV(0), *retval; |
| 466 | |
| 467 | sv_setpvf(command, "$string = '%s'; ($string =~ %s)", |
| 468 | SvPV_nolen(*string), pattern); |
| 469 | |
| 470 | retval = my_eval_sv(command, TRUE); |
| 471 | SvREFCNT_dec(command); |
| 472 | |
| 473 | *string = get_sv("string", 0); |
| 474 | return SvIV(retval); |
| 475 | } |
| 476 | |
| 477 | /** matches(string, pattern, matches) |
| 478 | ** |
| 479 | ** Used for matches in a list context. |
| 480 | ** |
| 481 | ** Returns the number of matches, |
| 482 | ** and fills in **matches with the matching substrings |
| 483 | **/ |
| 484 | |
| 485 | SSize_t matches(SV *string, char *pattern, AV **match_list) |
| 486 | { |
| 487 | SV *command = newSV(0); |
| 488 | SSize_t num_matches; |
| 489 | |
| 490 | sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)", |
| 491 | SvPV_nolen(string), pattern); |
| 492 | |
| 493 | my_eval_sv(command, TRUE); |
| 494 | SvREFCNT_dec(command); |
| 495 | |
| 496 | *match_list = get_av("array", 0); |
| 497 | num_matches = av_top_index(*match_list) + 1; |
| 498 | |
| 499 | return num_matches; |
| 500 | } |
| 501 | |
| 502 | main (int argc, char **argv, char **env) |
| 503 | { |
| 504 | char *embedding[] = { "", "-e", "0" }; |
| 505 | AV *match_list; |
| 506 | I32 num_matches, i; |
| 507 | SV *text; |
| 508 | |
| 509 | PERL_SYS_INIT3(&argc,&argv,&env); |
| 510 | my_perl = perl_alloc(); |
| 511 | perl_construct(my_perl); |
| 512 | perl_parse(my_perl, NULL, 3, embedding, NULL); |
| 513 | PL_exit_flags |= PERL_EXIT_DESTRUCT_END; |
| 514 | |
| 515 | text = newSV(0); |
| 516 | sv_setpv(text, "When he is at a convenience store and the " |
| 517 | "bill comes to some amount like 76 cents, Maynard is " |
| 518 | "aware that there is something he *should* do, something " |
| 519 | "that will enable him to get back a quarter, but he has " |
| 520 | "no idea *what*. He fumbles through his red squeezey " |
| 521 | "changepurse and gives the boy three extra pennies with " |
| 522 | "his dollar, hoping that he might luck into the correct " |
| 523 | "amount. The boy gives him back two of his own pennies " |
| 524 | "and then the big shiny quarter that is his prize. " |
| 525 | "-RICHH"); |
| 526 | |
| 527 | if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/ |
| 528 | printf("match: Text contains the word 'quarter'.\n\n"); |
| 529 | else |
| 530 | printf("match: Text doesn't contain the word 'quarter'.\n\n"); |
| 531 | |
| 532 | if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/ |
| 533 | printf("match: Text contains the word 'eighth'.\n\n"); |
| 534 | else |
| 535 | printf("match: Text doesn't contain the word 'eighth'.\n\n"); |
| 536 | |
| 537 | /** Match all occurrences of /wi../ **/ |
| 538 | num_matches = matches(text, "m/(wi..)/g", &match_list); |
| 539 | printf("matches: m/(wi..)/g found %d matches...\n", num_matches); |
| 540 | |
| 541 | for (i = 0; i < num_matches; i++) |
| 542 | printf("match: %s\n", |
| 543 | SvPV_nolen(*av_fetch(match_list, i, FALSE))); |
| 544 | printf("\n"); |
| 545 | |
| 546 | /** Remove all vowels from text **/ |
| 547 | num_matches = substitute(&text, "s/[aeiou]//gi"); |
| 548 | if (num_matches) { |
| 549 | printf("substitute: s/[aeiou]//gi...%lu substitutions made.\n", |
| 550 | (unsigned long)num_matches); |
| 551 | printf("Now text is: %s\n\n", SvPV_nolen(text)); |
| 552 | } |
| 553 | |
| 554 | /** Attempt a substitution **/ |
| 555 | if (!substitute(&text, "s/Perl/C/")) { |
| 556 | printf("substitute: s/Perl/C...No substitution made.\n\n"); |
| 557 | } |
| 558 | |
| 559 | SvREFCNT_dec(text); |
| 560 | PL_perl_destruct_level = 1; |
| 561 | perl_destruct(my_perl); |
| 562 | perl_free(my_perl); |
| 563 | PERL_SYS_TERM(); |
| 564 | } |
| 565 | |
| 566 | which produces the output (again, long lines have been wrapped here) |
| 567 | |
| 568 | match: Text contains the word 'quarter'. |
| 569 | |
| 570 | match: Text doesn't contain the word 'eighth'. |
| 571 | |
| 572 | matches: m/(wi..)/g found 2 matches... |
| 573 | match: will |
| 574 | match: with |
| 575 | |
| 576 | substitute: s/[aeiou]//gi...139 substitutions made. |
| 577 | Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts, |
| 578 | Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt |
| 579 | bck qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd |
| 580 | gvs th by thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct |
| 581 | mnt. Th by gvs hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s |
| 582 | hs prz. -RCHH |
| 583 | |
| 584 | substitute: s/Perl/C...No substitution made. |
| 585 | |
| 586 | =head2 Fiddling with the Perl stack from your C program |
| 587 | |
| 588 | When trying to explain stacks, most computer science textbooks mumble |
| 589 | something about spring-loaded columns of cafeteria plates: the last |
| 590 | thing you pushed on the stack is the first thing you pop off. That'll |
| 591 | do for our purposes: your C program will push some arguments onto "the Perl |
| 592 | stack", shut its eyes while some magic happens, and then pop the |
| 593 | results--the return value of your Perl subroutine--off the stack. |
| 594 | |
| 595 | First you'll need to know how to convert between C types and Perl |
| 596 | types, with newSViv() and sv_setnv() and newAV() and all their |
| 597 | friends. They're described in L<perlguts> and L<perlapi>. |
| 598 | |
| 599 | Then you'll need to know how to manipulate the Perl stack. That's |
| 600 | described in L<perlcall>. |
| 601 | |
| 602 | Once you've understood those, embedding Perl in C is easy. |
| 603 | |
| 604 | Because C has no builtin function for integer exponentiation, let's |
| 605 | make Perl's ** operator available to it (this is less useful than it |
| 606 | sounds, because Perl implements ** with C's I<pow()> function). First |
| 607 | I'll create a stub exponentiation function in I<power.pl>: |
| 608 | |
| 609 | sub expo { |
| 610 | my ($a, $b) = @_; |
| 611 | return $a ** $b; |
| 612 | } |
| 613 | |
| 614 | Now I'll create a C program, I<power.c>, with a function |
| 615 | I<PerlPower()> that contains all the perlguts necessary to push the |
| 616 | two arguments into I<expo()> and to pop the return value out. Take a |
| 617 | deep breath... |
| 618 | |
| 619 | #include <EXTERN.h> |
| 620 | #include <perl.h> |
| 621 | |
| 622 | static PerlInterpreter *my_perl; |
| 623 | |
| 624 | static void |
| 625 | PerlPower(int a, int b) |
| 626 | { |
| 627 | dSP; /* initialize stack pointer */ |
| 628 | ENTER; /* everything created after here */ |
| 629 | SAVETMPS; /* ...is a temporary variable. */ |
| 630 | PUSHMARK(SP); /* remember the stack pointer */ |
| 631 | XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */ |
| 632 | XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */ |
| 633 | PUTBACK; /* make local stack pointer global */ |
| 634 | call_pv("expo", G_SCALAR); /* call the function */ |
| 635 | SPAGAIN; /* refresh stack pointer */ |
| 636 | /* pop the return value from stack */ |
| 637 | printf ("%d to the %dth power is %d.\n", a, b, POPi); |
| 638 | PUTBACK; |
| 639 | FREETMPS; /* free that return value */ |
| 640 | LEAVE; /* ...and the XPUSHed "mortal" args.*/ |
| 641 | } |
| 642 | |
| 643 | int main (int argc, char **argv, char **env) |
| 644 | { |
| 645 | char *my_argv[] = { "", "power.pl" }; |
| 646 | |
| 647 | PERL_SYS_INIT3(&argc,&argv,&env); |
| 648 | my_perl = perl_alloc(); |
| 649 | perl_construct( my_perl ); |
| 650 | |
| 651 | perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL); |
| 652 | PL_exit_flags |= PERL_EXIT_DESTRUCT_END; |
| 653 | perl_run(my_perl); |
| 654 | |
| 655 | PerlPower(3, 4); /*** Compute 3 ** 4 ***/ |
| 656 | |
| 657 | perl_destruct(my_perl); |
| 658 | perl_free(my_perl); |
| 659 | PERL_SYS_TERM(); |
| 660 | } |
| 661 | |
| 662 | |
| 663 | |
| 664 | Compile and run: |
| 665 | |
| 666 | % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
| 667 | |
| 668 | % power |
| 669 | 3 to the 4th power is 81. |
| 670 | |
| 671 | =head2 Maintaining a persistent interpreter |
| 672 | |
| 673 | When developing interactive and/or potentially long-running |
| 674 | applications, it's a good idea to maintain a persistent interpreter |
| 675 | rather than allocating and constructing a new interpreter multiple |
| 676 | times. The major reason is speed: since Perl will only be loaded into |
| 677 | memory once. |
| 678 | |
| 679 | However, you have to be more cautious with namespace and variable |
| 680 | scoping when using a persistent interpreter. In previous examples |
| 681 | we've been using global variables in the default package C<main>. We |
| 682 | knew exactly what code would be run, and assumed we could avoid |
| 683 | variable collisions and outrageous symbol table growth. |
| 684 | |
| 685 | Let's say your application is a server that will occasionally run Perl |
| 686 | code from some arbitrary file. Your server has no way of knowing what |
| 687 | code it's going to run. Very dangerous. |
| 688 | |
| 689 | If the file is pulled in by C<perl_parse()>, compiled into a newly |
| 690 | constructed interpreter, and subsequently cleaned out with |
| 691 | C<perl_destruct()> afterwards, you're shielded from most namespace |
| 692 | troubles. |
| 693 | |
| 694 | One way to avoid namespace collisions in this scenario is to translate |
| 695 | the filename into a guaranteed-unique package name, and then compile |
| 696 | the code into that package using L<perlfunc/eval>. In the example |
| 697 | below, each file will only be compiled once. Or, the application |
| 698 | might choose to clean out the symbol table associated with the file |
| 699 | after it's no longer needed. Using L<perlapi/call_argv>, We'll |
| 700 | call the subroutine C<Embed::Persistent::eval_file> which lives in the |
| 701 | file C<persistent.pl> and pass the filename and boolean cleanup/cache |
| 702 | flag as arguments. |
| 703 | |
| 704 | Note that the process will continue to grow for each file that it |
| 705 | uses. In addition, there might be C<AUTOLOAD>ed subroutines and other |
| 706 | conditions that cause Perl's symbol table to grow. You might want to |
| 707 | add some logic that keeps track of the process size, or restarts |
| 708 | itself after a certain number of requests, to ensure that memory |
| 709 | consumption is minimized. You'll also want to scope your variables |
| 710 | with L<perlfunc/my> whenever possible. |
| 711 | |
| 712 | |
| 713 | package Embed::Persistent; |
| 714 | #persistent.pl |
| 715 | |
| 716 | use strict; |
| 717 | our %Cache; |
| 718 | use Symbol qw(delete_package); |
| 719 | |
| 720 | sub valid_package_name { |
| 721 | my($string) = @_; |
| 722 | $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg; |
| 723 | # second pass only for words starting with a digit |
| 724 | $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg; |
| 725 | |
| 726 | # Dress it up as a real package name |
| 727 | $string =~ s|/|::|g; |
| 728 | return "Embed" . $string; |
| 729 | } |
| 730 | |
| 731 | sub eval_file { |
| 732 | my($filename, $delete) = @_; |
| 733 | my $package = valid_package_name($filename); |
| 734 | my $mtime = -M $filename; |
| 735 | if(defined $Cache{$package}{mtime} |
| 736 | && |
| 737 | $Cache{$package}{mtime} <= $mtime) |
| 738 | { |
| 739 | # we have compiled this subroutine already, |
| 740 | # it has not been updated on disk, nothing left to do |
| 741 | print STDERR "already compiled $package->handler\n"; |
| 742 | } |
| 743 | else { |
| 744 | local *FH; |
| 745 | open FH, $filename or die "open '$filename' $!"; |
| 746 | local($/) = undef; |
| 747 | my $sub = <FH>; |
| 748 | close FH; |
| 749 | |
| 750 | #wrap the code into a subroutine inside our unique package |
| 751 | my $eval = qq{package $package; sub handler { $sub; }}; |
| 752 | { |
| 753 | # hide our variables within this block |
| 754 | my($filename,$mtime,$package,$sub); |
| 755 | eval $eval; |
| 756 | } |
| 757 | die $@ if $@; |
| 758 | |
| 759 | #cache it unless we're cleaning out each time |
| 760 | $Cache{$package}{mtime} = $mtime unless $delete; |
| 761 | } |
| 762 | |
| 763 | eval {$package->handler;}; |
| 764 | die $@ if $@; |
| 765 | |
| 766 | delete_package($package) if $delete; |
| 767 | |
| 768 | #take a look if you want |
| 769 | #print Devel::Symdump->rnew($package)->as_string, $/; |
| 770 | } |
| 771 | |
| 772 | 1; |
| 773 | |
| 774 | __END__ |
| 775 | |
| 776 | /* persistent.c */ |
| 777 | #include <EXTERN.h> |
| 778 | #include <perl.h> |
| 779 | |
| 780 | /* 1 = clean out filename's symbol table after each request, |
| 781 | 0 = don't |
| 782 | */ |
| 783 | #ifndef DO_CLEAN |
| 784 | #define DO_CLEAN 0 |
| 785 | #endif |
| 786 | |
| 787 | #define BUFFER_SIZE 1024 |
| 788 | |
| 789 | static PerlInterpreter *my_perl = NULL; |
| 790 | |
| 791 | int |
| 792 | main(int argc, char **argv, char **env) |
| 793 | { |
| 794 | char *embedding[] = { "", "persistent.pl" }; |
| 795 | char *args[] = { "", DO_CLEAN, NULL }; |
| 796 | char filename[BUFFER_SIZE]; |
| 797 | int exitstatus = 0; |
| 798 | |
| 799 | PERL_SYS_INIT3(&argc,&argv,&env); |
| 800 | if((my_perl = perl_alloc()) == NULL) { |
| 801 | fprintf(stderr, "no memory!"); |
| 802 | exit(1); |
| 803 | } |
| 804 | perl_construct(my_perl); |
| 805 | |
| 806 | PL_origalen = 1; /* don't let $0 assignment update the |
| 807 | proctitle or embedding[0] */ |
| 808 | exitstatus = perl_parse(my_perl, NULL, 2, embedding, NULL); |
| 809 | PL_exit_flags |= PERL_EXIT_DESTRUCT_END; |
| 810 | if(!exitstatus) { |
| 811 | exitstatus = perl_run(my_perl); |
| 812 | |
| 813 | while(printf("Enter file name: ") && |
| 814 | fgets(filename, BUFFER_SIZE, stdin)) { |
| 815 | |
| 816 | filename[strlen(filename)-1] = '\0'; /* strip \n */ |
| 817 | /* call the subroutine, |
| 818 | passing it the filename as an argument */ |
| 819 | args[0] = filename; |
| 820 | call_argv("Embed::Persistent::eval_file", |
| 821 | G_DISCARD | G_EVAL, args); |
| 822 | |
| 823 | /* check $@ */ |
| 824 | if(SvTRUE(ERRSV)) |
| 825 | fprintf(stderr, "eval error: %s\n", SvPV_nolen(ERRSV)); |
| 826 | } |
| 827 | } |
| 828 | |
| 829 | PL_perl_destruct_level = 0; |
| 830 | perl_destruct(my_perl); |
| 831 | perl_free(my_perl); |
| 832 | PERL_SYS_TERM(); |
| 833 | exit(exitstatus); |
| 834 | } |
| 835 | |
| 836 | Now compile: |
| 837 | |
| 838 | % cc -o persistent persistent.c \ |
| 839 | `perl -MExtUtils::Embed -e ccopts -e ldopts` |
| 840 | |
| 841 | Here's an example script file: |
| 842 | |
| 843 | #test.pl |
| 844 | my $string = "hello"; |
| 845 | foo($string); |
| 846 | |
| 847 | sub foo { |
| 848 | print "foo says: @_\n"; |
| 849 | } |
| 850 | |
| 851 | Now run: |
| 852 | |
| 853 | % persistent |
| 854 | Enter file name: test.pl |
| 855 | foo says: hello |
| 856 | Enter file name: test.pl |
| 857 | already compiled Embed::test_2epl->handler |
| 858 | foo says: hello |
| 859 | Enter file name: ^C |
| 860 | |
| 861 | =head2 Execution of END blocks |
| 862 | |
| 863 | Traditionally END blocks have been executed at the end of the perl_run. |
| 864 | This causes problems for applications that never call perl_run. Since |
| 865 | perl 5.7.2 you can specify C<PL_exit_flags |= PERL_EXIT_DESTRUCT_END> |
| 866 | to get the new behaviour. This also enables the running of END blocks if |
| 867 | the perl_parse fails and C<perl_destruct> will return the exit value. |
| 868 | |
| 869 | =head2 $0 assignments |
| 870 | |
| 871 | When a perl script assigns a value to $0 then the perl runtime will |
| 872 | try to make this value show up as the program name reported by "ps" by |
| 873 | updating the memory pointed to by the argv passed to perl_parse() and |
| 874 | also calling API functions like setproctitle() where available. This |
| 875 | behaviour might not be appropriate when embedding perl and can be |
| 876 | disabled by assigning the value C<1> to the variable C<PL_origalen> |
| 877 | before perl_parse() is called. |
| 878 | |
| 879 | The F<persistent.c> example above is for instance likely to segfault |
| 880 | when $0 is assigned to if the C<PL_origalen = 1;> assignment is |
| 881 | removed. This because perl will try to write to the read only memory |
| 882 | of the C<embedding[]> strings. |
| 883 | |
| 884 | =head2 Maintaining multiple interpreter instances |
| 885 | |
| 886 | Some rare applications will need to create more than one interpreter |
| 887 | during a session. Such an application might sporadically decide to |
| 888 | release any resources associated with the interpreter. |
| 889 | |
| 890 | The program must take care to ensure that this takes place I<before> |
| 891 | the next interpreter is constructed. By default, when perl is not |
| 892 | built with any special options, the global variable |
| 893 | C<PL_perl_destruct_level> is set to C<0>, since extra cleaning isn't |
| 894 | usually needed when a program only ever creates a single interpreter |
| 895 | in its entire lifetime. |
| 896 | |
| 897 | Setting C<PL_perl_destruct_level> to C<1> makes everything squeaky clean: |
| 898 | |
| 899 | while(1) { |
| 900 | ... |
| 901 | /* reset global variables here with PL_perl_destruct_level = 1 */ |
| 902 | PL_perl_destruct_level = 1; |
| 903 | perl_construct(my_perl); |
| 904 | ... |
| 905 | /* clean and reset _everything_ during perl_destruct */ |
| 906 | PL_perl_destruct_level = 1; |
| 907 | perl_destruct(my_perl); |
| 908 | perl_free(my_perl); |
| 909 | ... |
| 910 | /* let's go do it again! */ |
| 911 | } |
| 912 | |
| 913 | When I<perl_destruct()> is called, the interpreter's syntax parse tree |
| 914 | and symbol tables are cleaned up, and global variables are reset. The |
| 915 | second assignment to C<PL_perl_destruct_level> is needed because |
| 916 | perl_construct resets it to C<0>. |
| 917 | |
| 918 | Now suppose we have more than one interpreter instance running at the |
| 919 | same time. This is feasible, but only if you used the Configure option |
| 920 | C<-Dusemultiplicity> or the options C<-Dusethreads -Duseithreads> when |
| 921 | building perl. By default, enabling one of these Configure options |
| 922 | sets the per-interpreter global variable C<PL_perl_destruct_level> to |
| 923 | C<1>, so that thorough cleaning is automatic and interpreter variables |
| 924 | are initialized correctly. Even if you don't intend to run two or |
| 925 | more interpreters at the same time, but to run them sequentially, like |
| 926 | in the above example, it is recommended to build perl with the |
| 927 | C<-Dusemultiplicity> option otherwise some interpreter variables may |
| 928 | not be initialized correctly between consecutive runs and your |
| 929 | application may crash. |
| 930 | |
| 931 | See also L<perlxs/Thread-aware system interfaces>. |
| 932 | |
| 933 | Using C<-Dusethreads -Duseithreads> rather than C<-Dusemultiplicity> |
| 934 | is more appropriate if you intend to run multiple interpreters |
| 935 | concurrently in different threads, because it enables support for |
| 936 | linking in the thread libraries of your system with the interpreter. |
| 937 | |
| 938 | Let's give it a try: |
| 939 | |
| 940 | |
| 941 | #include <EXTERN.h> |
| 942 | #include <perl.h> |
| 943 | |
| 944 | /* we're going to embed two interpreters */ |
| 945 | |
| 946 | #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)" |
| 947 | |
| 948 | int main(int argc, char **argv, char **env) |
| 949 | { |
| 950 | PerlInterpreter *one_perl, *two_perl; |
| 951 | char *one_args[] = { "one_perl", SAY_HELLO }; |
| 952 | char *two_args[] = { "two_perl", SAY_HELLO }; |
| 953 | |
| 954 | PERL_SYS_INIT3(&argc,&argv,&env); |
| 955 | one_perl = perl_alloc(); |
| 956 | two_perl = perl_alloc(); |
| 957 | |
| 958 | PERL_SET_CONTEXT(one_perl); |
| 959 | perl_construct(one_perl); |
| 960 | PERL_SET_CONTEXT(two_perl); |
| 961 | perl_construct(two_perl); |
| 962 | |
| 963 | PERL_SET_CONTEXT(one_perl); |
| 964 | perl_parse(one_perl, NULL, 3, one_args, (char **)NULL); |
| 965 | PERL_SET_CONTEXT(two_perl); |
| 966 | perl_parse(two_perl, NULL, 3, two_args, (char **)NULL); |
| 967 | |
| 968 | PERL_SET_CONTEXT(one_perl); |
| 969 | perl_run(one_perl); |
| 970 | PERL_SET_CONTEXT(two_perl); |
| 971 | perl_run(two_perl); |
| 972 | |
| 973 | PERL_SET_CONTEXT(one_perl); |
| 974 | perl_destruct(one_perl); |
| 975 | PERL_SET_CONTEXT(two_perl); |
| 976 | perl_destruct(two_perl); |
| 977 | |
| 978 | PERL_SET_CONTEXT(one_perl); |
| 979 | perl_free(one_perl); |
| 980 | PERL_SET_CONTEXT(two_perl); |
| 981 | perl_free(two_perl); |
| 982 | PERL_SYS_TERM(); |
| 983 | } |
| 984 | |
| 985 | Note the calls to PERL_SET_CONTEXT(). These are necessary to initialize |
| 986 | the global state that tracks which interpreter is the "current" one on |
| 987 | the particular process or thread that may be running it. It should |
| 988 | always be used if you have more than one interpreter and are making |
| 989 | perl API calls on both interpreters in an interleaved fashion. |
| 990 | |
| 991 | PERL_SET_CONTEXT(interp) should also be called whenever C<interp> is |
| 992 | used by a thread that did not create it (using either perl_alloc(), or |
| 993 | the more esoteric perl_clone()). |
| 994 | |
| 995 | Compile as usual: |
| 996 | |
| 997 | % cc -o multiplicity multiplicity.c \ |
| 998 | `perl -MExtUtils::Embed -e ccopts -e ldopts` |
| 999 | |
| 1000 | Run it, Run it: |
| 1001 | |
| 1002 | % multiplicity |
| 1003 | Hi, I'm one_perl |
| 1004 | Hi, I'm two_perl |
| 1005 | |
| 1006 | =head2 Using Perl modules, which themselves use C libraries, from your C |
| 1007 | program |
| 1008 | |
| 1009 | If you've played with the examples above and tried to embed a script |
| 1010 | that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ |
| 1011 | library, this probably happened: |
| 1012 | |
| 1013 | |
| 1014 | Can't load module Socket, dynamic loading not available in this perl. |
| 1015 | (You may need to build a new perl executable which either supports |
| 1016 | dynamic loading or has the Socket module statically linked into it.) |
| 1017 | |
| 1018 | |
| 1019 | What's wrong? |
| 1020 | |
| 1021 | Your interpreter doesn't know how to communicate with these extensions |
| 1022 | on its own. A little glue will help. Up until now you've been |
| 1023 | calling I<perl_parse()>, handing it NULL for the second argument: |
| 1024 | |
| 1025 | perl_parse(my_perl, NULL, argc, my_argv, NULL); |
| 1026 | |
| 1027 | That's where the glue code can be inserted to create the initial contact |
| 1028 | between Perl and linked C/C++ routines. Let's take a look some pieces of |
| 1029 | I<perlmain.c> to see how Perl does this: |
| 1030 | |
| 1031 | static void xs_init (pTHX); |
| 1032 | |
| 1033 | EXTERN_C void boot_DynaLoader (pTHX_ CV* cv); |
| 1034 | EXTERN_C void boot_Socket (pTHX_ CV* cv); |
| 1035 | |
| 1036 | |
| 1037 | EXTERN_C void |
| 1038 | xs_init(pTHX) |
| 1039 | { |
| 1040 | char *file = __FILE__; |
| 1041 | /* DynaLoader is a special case */ |
| 1042 | newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file); |
| 1043 | newXS("Socket::bootstrap", boot_Socket, file); |
| 1044 | } |
| 1045 | |
| 1046 | Simply put: for each extension linked with your Perl executable |
| 1047 | (determined during its initial configuration on your |
| 1048 | computer or when adding a new extension), |
| 1049 | a Perl subroutine is created to incorporate the extension's |
| 1050 | routines. Normally, that subroutine is named |
| 1051 | I<Module::bootstrap()> and is invoked when you say I<use Module>. In |
| 1052 | turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl |
| 1053 | counterpart for each of the extension's XSUBs. Don't worry about this |
| 1054 | part; leave that to the I<xsubpp> and extension authors. If your |
| 1055 | extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()> |
| 1056 | for you on the fly. In fact, if you have a working DynaLoader then there |
| 1057 | is rarely any need to link in any other extensions statically. |
| 1058 | |
| 1059 | |
| 1060 | Once you have this code, slap it into the second argument of I<perl_parse()>: |
| 1061 | |
| 1062 | |
| 1063 | perl_parse(my_perl, xs_init, argc, my_argv, NULL); |
| 1064 | |
| 1065 | |
| 1066 | Then compile: |
| 1067 | |
| 1068 | % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
| 1069 | |
| 1070 | % interp |
| 1071 | use Socket; |
| 1072 | use SomeDynamicallyLoadedModule; |
| 1073 | |
| 1074 | print "Now I can use extensions!\n"' |
| 1075 | |
| 1076 | B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code. |
| 1077 | |
| 1078 | % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c |
| 1079 | % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts` |
| 1080 | % cc -c interp.c `perl -MExtUtils::Embed -e ccopts` |
| 1081 | % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts` |
| 1082 | |
| 1083 | Consult L<perlxs>, L<perlguts>, and L<perlapi> for more details. |
| 1084 | |
| 1085 | =head2 Using embedded Perl with POSIX locales |
| 1086 | |
| 1087 | (See L<perllocale> for information about these.) |
| 1088 | When a Perl interpreter normally starts up, it tells the system it wants |
| 1089 | to use the system's default locale. This is often, but not necessarily, |
| 1090 | the "C" or "POSIX" locale. Absent a S<C<"use locale">> within the perl |
| 1091 | code, this mostly has no effect (but see L<perllocale/Not within the |
| 1092 | scope of "use locale">). Also, there is not a problem if the |
| 1093 | locale you want to use in your embedded Perl is the same as the system |
| 1094 | default. However, this doesn't work if you have set up and want to use |
| 1095 | a locale that isn't the system default one. Starting in Perl v5.20, you |
| 1096 | can tell the embedded Perl interpreter that the locale is already |
| 1097 | properly set up, and to skip doing its own normal initialization. It |
| 1098 | skips if the environment variable C<PERL_SKIP_LOCALE_INIT> is set (even |
| 1099 | if set to 0 or C<"">). A Perl that has this capability will define the |
| 1100 | C pre-processor symbol C<HAS_SKIP_LOCALE_INIT>. This allows code that |
| 1101 | has to work with multiple Perl versions to do some sort of work-around |
| 1102 | when confronted with an earlier Perl. |
| 1103 | |
| 1104 | =head1 Hiding Perl_ |
| 1105 | |
| 1106 | If you completely hide the short forms of the Perl public API, |
| 1107 | add -DPERL_NO_SHORT_NAMES to the compilation flags. This means that |
| 1108 | for example instead of writing |
| 1109 | |
| 1110 | warn("%d bottles of beer on the wall", bottlecount); |
| 1111 | |
| 1112 | you will have to write the explicit full form |
| 1113 | |
| 1114 | Perl_warn(aTHX_ "%d bottles of beer on the wall", bottlecount); |
| 1115 | |
| 1116 | (See L<perlguts/"Background and PERL_IMPLICIT_CONTEXT"> for the explanation |
| 1117 | of the C<aTHX_>. ) Hiding the short forms is very useful for avoiding |
| 1118 | all sorts of nasty (C preprocessor or otherwise) conflicts with other |
| 1119 | software packages (Perl defines about 2400 APIs with these short names, |
| 1120 | take or leave few hundred, so there certainly is room for conflict.) |
| 1121 | |
| 1122 | =head1 MORAL |
| 1123 | |
| 1124 | You can sometimes I<write faster code> in C, but |
| 1125 | you can always I<write code faster> in Perl. Because you can use |
| 1126 | each from the other, combine them as you wish. |
| 1127 | |
| 1128 | |
| 1129 | =head1 AUTHOR |
| 1130 | |
| 1131 | Jon Orwant <F<orwant@media.mit.edu>> and Doug MacEachern |
| 1132 | <F<dougm@covalent.net>>, with small contributions from Tim Bunce, Tom |
| 1133 | Christiansen, Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya |
| 1134 | Zakharevich. |
| 1135 | |
| 1136 | Doug MacEachern has an article on embedding in Volume 1, Issue 4 of |
| 1137 | The Perl Journal ( http://www.tpj.com/ ). Doug is also the developer of the |
| 1138 | most widely-used Perl embedding: the mod_perl system |
| 1139 | (perl.apache.org), which embeds Perl in the Apache web server. |
| 1140 | Oracle, Binary Evolution, ActiveState, and Ben Sugars's nsapi_perl |
| 1141 | have used this model for Oracle, Netscape and Internet Information |
| 1142 | Server Perl plugins. |
| 1143 | |
| 1144 | =head1 COPYRIGHT |
| 1145 | |
| 1146 | Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant. All |
| 1147 | Rights Reserved. |
| 1148 | |
| 1149 | This document may be distributed under the same terms as Perl itself. |